1. Field of the Invention
The invention relates to a method of dry etching for processing the surface of an object to be processed into a concavo-convex pattern, a method of manufacturing a magnetic recording medium by using the same, and a magnetic recording medium having a recording layer formed in a concavo-convex pattern.
2. Description of the Related Art
Conventionally, in the fields of semiconductors and the like, dry etching has been widely used for processing the surface of an object to be processed into a concavo-convex pattern. In the field of information recording media, there have also been the needs to process the surface of an object to be processed into a concavo-convex pattern. For the purpose of this processing, the use of dry etching has thus been expected.
For example, magnetic recording media such as a hard disk have made significant growths in areal density through such improvements as finer magnetic particles to constitute the recording layers, modifications of materials, and finer head processing. Further enhancement of the areal density in the future is also expected. Nevertheless, the enhancement of the areal density with conventional improvement techniques is approaching its limit as the advent of such problems as limitations in the head processing, accidental recording of information onto other tracks adjacent to an intended track due to spreading magnetic fields, and crosstalk. In view of this, there have been proposed such magnetic recording media as a discrete track medium and a patterned medium (for example, see Japanese Patent Laid-Open Publication No. Hei 9-97419) as candidates for magnetic recording media that are capable of further enhancement in areal density. In these media, the recording layer is formed in a predetermined concavo-convex pattern so that the convex portions constitute recording elements. It is then expected to use dry etching in order to process the recording layer into a concavo-convex pattern.
Among the dry etching techniques available for processing the recording layer, made of a magnetic material, into a concavo-convex pattern is reactive ion etching in which CO (carbon monoxide) gas having a nitrogen-containing gas such as NH3 (ammonia) gas added thereto is used as the reactive gas (for example, see Japanese Patent Laid-Open Publication No. Hei 12-322710). To process the recording layer (to-be-etched layer) by dry etching, a mask layer must be processed into the concavo-convex pattern. The mask layer, in turn, can also be processed by using a dry etching technique. For example, a resist layer is formed on the mask layer, and the resist layer is processed into a concavo-convex pattern by a lithographic method or the like which is used in the field of semiconductors. Then, the mask layer can be processed into the concavo-convex pattern by removing parts of the mask layer under the concave portions by dry etching. Alternatively, the resist layer may be formed on the mask layer with another mask layer interposed therebetween. These mask layers can be dry etched from the resist-layer side in succession to process the mask layer lying on the to-be-etched layer into the concavo-convex pattern.
The to-be-etched layer can be surely processed into a predetermined concavo-convex pattern by dry etching. It is difficult, however, to shape the sides 102A of the convex portions 102 of the to-be-etched layer 100 generally perpendicular to the surface as shown in FIG. 12. In fact, as shown in FIG. 13, the sides 102A are processed into tapered shapes tilting toward the surface, thereby causing a difference between the intended shape and the actually-processed shape. More specifically, in the dry etching as shown in FIG. 13, some of the processing gas approaches the object to be processed with slight tilts from the perpendicular direction. Consequently, even if the edges of the to-be-etched areas of the to-be-etched layer 100 are exposed from the mask 104, they are hidden under the mask 104 from some of the processing gas. Those areas can thus be etched slower than the other areas, seemingly contributing to the tapered shapes of the sides 102A.
Moreover, since the mask layer is also processed by dry etching as mentioned above, its convex portions are also shaped into tapered sides. As a result, the concavo-convex pattern of the resist layer and the mask layer on the surface side is transferred to the to-be-etched layer with gradual increases in the convex portion widths. The greater the taper angle of the sides of the convex portions of the mask layer is, the lower precision the concavo-convex pattern is transferred to the to-be-etched layer with. Furthermore, if the taper angle of the sides of the convex portions of the mask layer is too large, V-shaped grooves having continuous sides may be formed on the to-be-etched layer. This sometimes limits the progress of etching, failing to process into a desired depth. For example, in the above-mentioned magnetic recording media such as a discrete medium and a patterned medium, it is sometimes impossible to divide the recording layer due to the formation of V grooves shallower than the thickness of the recording layer.
As the pattern to be etched becomes finer, the difference between the intended shape and the actually-processed shape tends to have a relatively higher impact on the characteristics of the products. For example, in such magnetic recording media as a discrete track medium and a patterned medium, the recording elements approach each other when the sides of the recording elements are processed into tapered shapes. This facilitates the problem of accidental recording of information onto other tracks adjacent to the intended track and the problem of crosstalk, thereby deteriorating the magnetic characteristics. This has given rise to a demand for a method of dry etching capable of processing the surface of the object to be processed into a concavo-convex pattern so that the sides of the convex portions are shaped generally perpendicular to the surface.
Incidentally, such magnetic recording media as a discrete track medium and a patterned medium may deteriorate in magnetic characteristics when the recording elements are exposed to the processing gas during processing or exposed to the air after the processing. Then, a method of dry etching capable of protecting the surface of the object to be processed while processing the surface of the object to be processed into a concavo-convex pattern has also be demanded.
Now, suppose that reactive ion etching is performed as the dry etching for processing the mask layer into a concavo-convex pattern, and the mask layer keeps being processed even after the mask layer is processed up to the bottom. Here, the side areas of the convex portions of the mask layer can be surely removed to reduce the width of the convex portions of the mask layer and the taper angle of the sides. Processing the mask layer thus longer, however, requires that the other mask layers and resist layers to be formed thereon be made accordingly thicker. The resist layer formed thicker may sometimes cause deformation or collapse of its convex portions, with a drop in the processing accuracy instead.
Considering that the sides of the convex portions of the mask layer are processed into tapered shapes, the outermost mask layer or resist layer may be provided with a concavo-convex pattern having convex portions narrower than those of the intended concavo-convex pattern of the to-be-etched layer. This can make it possible to process the to-be-etched layer into the desired etching pattern. Nevertheless, if the concavo-convex pattern has smaller pitches, the outermost mask layer or resist layer must have convex portions of excessively smaller widths. This sometimes facilitates deformation or collapse of the convex portions, or even makes it difficult to form the convex portions.